Lt. Frank Bullitt (Steve McQueen) is called on by D.A. to protect a star witness in a case that he hopes will take him into politics. The subject is a Johnny Ross, a mob accountant who mad off with a load of money and sought protection from the law. Bullitt puts Ross up in a hotel until the hearing, and puts several police on rotating guard. In the middle of the night, two assassins make their way into the room, kill Ross, and wound several officers. Worried that his career is ruined, the D.A. hopes to make an example out of Bullitt, even while Bullitt realizes there's more to this case then what appears to be.